The present invention relates to a photopolymerizable mixture that contains a polymer binder, a polymerizable compound having at least one terminal ethylenic double bond and a boiling point above about 100.degree. C. at normal pressure and a photoinitiator combination. The mixture is suitable for the preparation of recording materials, in particular of printing plates and photoresists.
EP 138,187 discloses photopolymerizable mixtures that contain, as photoinitiators, a combination of a hexaarylbisimidazole with an N-heterocyclic compound substituted by p-dialkylaminophenyl groups. These substituted N-heterocyclic compounds have the disadvantage that they are readily soluble in acids and, for example, when used as plating resists are extracted from the acid baths and contaminate the latter.
JP 55/75 405 describes 2-pyrazoline derivatives having substituents in the 1-, 3-, 4- and/or 5-position as photoinitiators, which are optionally combined with compounds containing aromatic keto groups. These initiators and initiator combinations give mixtures which are not sufficiently photosensitive for use in practice.
DE 3,019,211 relates to sensitization of iodonium and sulfonium compounds, which act as photoinitiators, with polyarylpyrazolines. It also relates to combinations of these mixtures with monomers which can be polymerized by free radical polymerization. The photosensitivity of these mixtures is inadequate.